This invention relates to a multiple heterojunction semiconductor laser of a stripe geometry structure.
A strip geometry multiple heterostructure semiconductor laser is generally desirable because of its low threshold exciting current density and its capability of producing an optical output or laser beam with a high efficiency even at room temperature. A laser is often required to have a narrow stripe width so as to produce a small-diameter beam for use in, for example, an optical fiber communication system. The conventional lasers of the type described, however, exhibit various defects. The laser has to be put into operation by a considerably large exciting electric current and yet produce a small-power optical output with a low efficiency and nonlinear optical output versus exciting current characeteristics, particularly when the laser has a narrow stripe width. The laser is not sufficiently reliable because it is liable to produce an optical output of higher-order transverse modes, and therefore, become unstable in operation particularly when the laser has a wide stripe width. A buried heterostructure laser is capable of producing a small-diameter beam but is difficult to manufacture. In a laser known as a TJS laser, laser oscillation is absorbed to a considerable extent. The buried heterostructure and TJS lasers are liable to deteriorate and are therefore also unreliable. In some of the conventional lasers, confinement of the laser oscillation is not well achieved.